The invention relates to a sheet metal component made of a press-hardened steel sheet material or a press-hardened sheet metal component, in particular, to a vehicle body component for a motor vehicle.
The invention further relates to a component assembly comprising several components for a motor vehicle body, and also to a motor vehicle body.
A press-hardened sheet metal component is a sheet metal part made of press-hardened steel sheet material. A press-hardened sheet metal component is therefore a flat component produced by press-hardening or mold-hardening of steel sheet material. For the press-hardening, the steel sheet material is heated to an austenization temperature and is subsequently molded in a press-hardening tool, and in the process is simultaneously rapidly cooled, whereby considerable increases of strength are achieved (for example, tensile strengths of up to 1,300 MPa and more are reached). From the prior art, various methods for press-hardening as well as corresponding devices are known. In a representative fashion, reference is made to the detailed explanations in German Patent Document DE 10 2011 053 698 B3.
However, the high strength of press-hardened sheet metal components is associated with relatively low ductility or elongation at break. Press-hardened sheet metal components therefore tend to break even after a slight deformation in the event of an accident, which rather reduces the amount of collision energy that can be absorbed or reduced by a deformation in the event of an accident or the like. Furthermore, uncontrolled fractures may occur in the case of accident-caused deformations, which may lead to formation of sharp edges and/or open gaps and can thereby pose a considerable risk of injury.
In German Patent Document DE 20 2012 000 616 U1, a structural and/or vehicle body component for a motor vehicle is suggested, which is produced by thermoforming and press-hardening. After the press-hardening, this component has at least two structural regions of varying strength and/or different ductility. A first region of the component essentially has a martensitic structure, and a second region, which has a lower strength and/or higher ductility in comparison with the first region, has an essentially bainitic structure. As a result, it is achieved that, in regions, the component can be designed for individual loads, particularly crash loads. However, the production of such components requires high expenditures and, at times, such components are extremely inefficient.
Concerning the prior art, reference is further made to German Patent Document DE 10 2012 024 626 A1, which suggests a bainitization of the press-molded sheet metal component in a galvanizing bath, and to German Patent Document DE 10 2012 201 267 A1, which suggests an annealing of press-hardened components that follows the press-hardening.
By means of the invention, alternatives are to be created to the measures and approaches known from the prior art.
This and other objects are achieved by a press-hardened sheet metal component and by a component assembly as well as by a motor vehicle body, which has the at least one sheet metal component in accordance with embodiments of the invention.
The press-hardened sheet metal component according to the invention has at least one overhardened component region, which is provided for acting as a predetermined breaking point in the event of a crash-caused load.
An overhardened component region is a region or surface section of the sheet metal component in which the sheet metal material has a clearly higher hardness or strength and a significantly lower ductility than the other regions. In an overhardened component region, the steel sheet material has an essentially pure martensitic structure or a structure with a very high martensitic structure proportion, whereas a mixed structure is present outside the overhardened component region. Such mixed structure, in addition to martensitic structure parts, may also, for example, have bainitic and/or ferritic structure parts.
The sheet metal component according to the invention is the most brittle in an overhardened component region or has the lowest ductility there. In the case of crash loads and resulting crash-caused deformations, the press-hardened sheet metal component according to the invention will tear and/or break first in such an overhardened component region. The press-hardened sheet metal component according to the invention therefore has at least one overhardened component region, which forms or represents a predetermined, i.e. position-predefined breaking point.
The invention therefore takes on a new direction in that, in contrast to the prior art, it is not attempted to avoid tears and/or fractures by increasing ductility, but, in contrast to the previous approach, to permit tears and/or fractures at defined points by a targeted local reduction of ductility (or by embrittlement by means of overhardening). This provides the designer and/or developer with new possibilities for designing crash-relevant vehicle body components and also superior vehicle body structures.
An overhardened component region can be generated when press-hardening or during the press-hardening. For example, the cooling device of the used press-hardening tool in the respective section may be designed for a locally stronger or more intensive cooling, Furthermore, in the concerned tool section, the surface pressure may be locally increased, in order to achieve a better heat transfer. Special tool materials, which permit a good heat conduction, may also be used for the concerned tool section.
In contrast to the approaches so far described in the prior art, which aim at an increase of ductility, a “reverse temperature control” takes place which aims at a reduction of ductility. The at least one overhardened component region can therefore be produced directly during the press-hardening of the previously heated steel sheet material, so that advantageously no additional working step, such as a thermal treatment following the press-hardening, will be required.
In particular, the steel sheet material is a manganese boron steel, such as 16MnB5, 20MnB5 or 22MnB5. The sheet thickness of the steel sheet material is preferably in a range of from 0.5 mm to 6.0 mm, particularly in a range of 0.8 mm to 3.0 mm. The sheet metal component according to the invention preferably has a substantially homogeneous sheet thickness, in which case, by using so-called tailored blanks, the sheet metal component according to the invention may also have an inhomogeneous sheet thickness.
Outside an overhardened component region, the sheet metal material of the sheet metal component according to the invention may have a substantially homogenous strength, which particularly is in a strength range of from 1,300 MPa to 1,500 MPa.
Outside an overhardened component region, the sheet metal material may also have different strengths. This means that the sheet metal component according to the invention, as described in German Patent Document DE 20 2012 000 616 U1, has at least one first component region and at least one second component region with a different strength and/or different ductility (in which case, also at least one unhardened or only slightly hardened region can be provided), as well as also at least one third overhardened component region. A first region may, for example, have strength of from 300 MPa to 500 MPa, and a second region may, for example, have a strength of from 1,300 MPa to 1,500 MPa. In the case of a crash load, a ductile first region has a good deformation behavior, whereas an overhardened third region acts as a predetermined breaking point. The sheet metal component according to the invention may be designed such that, in the case of a crash load, ductile regions are deformed first and, in a time-staggered manner, a tear and/or fracture is created in at least one overhardened region.
In an overhardened component region, the sheet metal material may have a strength which is at least by 100 MPa, preferably at least by 200 MPa, particularly preferably at least by 300 MPa and particularly at least by 400 MPa above the highest sheet metal or material strength outside the overhardened component region. The strength in an overhardened component region may, for example, amount to at least 1,600 MPa, preferably at least 1,700 MPa, particularly preferably at least 1,800 MPa and particularly at least 1,900 MPa. The strength in an overhardened component region may also amount to up to 2,000 MPa and more. Preferably, the high strength in an overhardened component region is homogeneous.
An overhardened component region may extend from an outer edge of the sheet metal component to at least another outer edge of the sheet metal component. An overhardened component region preferably extends in a ribbon-type fashion between two outer edges of the sheet metal component. In the event of a crash load, a tear and/or fracture will occur at the predetermined breaking point between the respective outer edges, which is formed by the overhardening of the sheet metal material, in which case a complete separation may possibly take place. However, a breaking-in-two and/or tearing-in-two is not absolutely necessary.
The press-hardened sheet metal component according to the invention, in particular, is a vehicle body component for a motor vehicle, such as a transverse support, a roof bow, a side skirt, a longitudinal support, an A-pillar or B-pillar, an engine mount, or the like. Particularly preferably, it is a reinforcing or stiffening part for a motor vehicle body, such as a side skirt reinforcement, a longitudinal support reinforcement, a pillar reinforcement, a tunnel reinforcement or the like. However, the press-hardened sheet metal component according to the invention may also be a chassis component.
The component assembly according to the invention has at least one press-hardened sheet metal component according to the invention which, in the event of crash loads can tear and/or break in at least one overhardened component region, in order to thereby deflect or divert collision energy in a targeted manner into other components and particularly into adjacent components of the component assembly. It is preferably provided that at least one other and particularly an adjacent component is designed as an energy absorption element, which can absorb and reduce collision energy by defined deformation (i.e. by deformation with predetermined deformation possibilities).
In the event of an accident, crash energy (impact energy) is therefore diverted in a targeted manner and is, for example, deflected away from vehicle occupants, which is made possible by the tearing and/or breaking of a press-hardened sheet metal component according to the invention in at least one predetermined breaking point predefined by overhardening. In contrast, it is attempted in the prior art to avoid such a tearing and/or breaking and/or reduce collision energy by allowing deformation of the press-hardened sheet metal component.
A component assembly according to the invention is, for example, a composite component formed of several components, (for example, a vehicle body component constructed as a composite component) for a motor vehicle body, as described, for example, in German Patent Document DE 10 2013 007 805 A1. However, a component assembly according to the invention may also be a component of a motor vehicle body or a constructionally integrated vehicle body structure region. Either way, a component assembly according to the invention includes further components which are appropriately joined with the press-hardened sheet metal component according to the invention, and which may, for example, be castings, sheet metal components or sheet metal parts (particularly also with different strengths), profile parts, plastic parts or plastic compound parts (for example, CFC parts, GFRP parts and/or the like. Each of these components may be designed as an energy absorption element.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.